3.Results and Discussion
In the paddy map based on satellite data analysis (Fig. 1), border polygons were overlapped and area totaled for each city. In 16 cities in Ibaraki Prefecture, lotus paddies exceed 10 ha. Areas based on satellite data were compared with administrative statistics and a significant correlation found (R2=098). Values based on satellite data were 25% smaller than statistics, however. Since the area of individual lotus paddy groups was small and their borders with other land covers long, we concluded that mixel areas are large and lotus paddy areas small. Rice paddy area based on satellite data was also compared with statistics and a significant correlation found (R2=0.98). Regional differences in rice growing throughout Kanto plain, however, greatly influenced extraction accuracy, making it difficult to map rice paddies based entirely on satellite data.


Fig. 1 A paddy map based on satellite data.
(a) Original Landsat TM image
(b) Distribution of lotus paddy (black) and rice paddy (white)

Fig.2 A marshand map based on satellite data.
(a) Original Landsat TM image
(b) Distribution of lotus paddy (black) and rice paddy (white)
Based on the rice paddy map made from a land use map dataset of numeric land information we recorded methane emission for rice paddies (Fig. 3). Border polygons were overlapped and regional methane emission calculated for each prefecture, resulting in values 20% or more greater than values previously reported (Japan Soil Association, 1996). Land use data showed rice paddy area greater than that actually cultivated. This report only shows the amount of methane emission in each prefecture, and our results should prove to understanding regional methane emission despite such inaccuracies.


Fig. 3 Estimation of methane emission.
(a) A paddy map based on numeric land information issued by Japanese National Land Agency.
(b) Classification of methane emission from rice paddies.

High :	25~ g/m2/year
Middle :	10~25g/m2/year
Low :	~10g/m2/year

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